Several cable telephony systems have been proposed for combining telephony, video, and data information over a cable distribution network taking advantage of the existing high bandwidth capabilities of cable television (CATV) operators which have an existing HFC distribution network to subscriber premises that could carry such diverse services. The goal of internet protocol (IP) telephony employing cable modem technology is to combine telephony, video, and data signals over a cable distribution infrastructure.
A primary goal of the various proposed cable telephony systems is to provide backwards compatibility with the existing telephone system infrastructure. Among other things, this requires that a subscriber to a cable telephony system be able to plug their existing telephone unit into the cable telephony system and have it operate in the same manner of operation as that provided by the public switched telephone network (PSTN). However, this basic requirement presents a significant number of issues to the design of the cable subscriber unit, e.g., existing telephones are presently powered through the telephone line provided by the PSTN, as opposed to the premise powered television units which are employed by subscribers to the cable distribution network. The line powered subscriber unit is an important component of the existing PSTN, which provides a so-called lifeline feature that allows a subscriber to make an emergency telephone call even when the premise power is down. Accordingly, whereas conventional packet telephony systems require the subscriber unit to be always powered on and listening, which results in maximum power consumption, it would be desirable to allow a subscriber unit to implement power saving techniques. A low power consumption packet telephony subscriber unit may therefore be line powered, enabling the lifeline packet telephony service.
The most conventional existing telephone service, sometimes referred to as "plain old telephone service" (POTS) requires the operator to provide loop current, i.e., 24 VDC at 25 mA, when the subscribers' telephone is in an off-hook state. If one multiplies the POTS power requirement by the potential number of subscribers in a cable telephony system however, the power management problem is significant. This problem is especially acute because existing cable television systems are not designed to handle such power distribution requirements and are not required to provide power to any subscriber equipment Whereas some power management concepts, such as providing a sleep mode and periodic broadcast channels, are employed in various wireless telephony systems and some cable distribution networks employing time division multiple access (TDMA) circuit-oriented systems providing periodic data transmissions, the problem is not so readily understood or overcome in an IP telephony environment in which data packets are communicated on an asynchronous basis by the nature of the internet infrastructure.
Cable telephony subscriber units employ a radio frequency (RF) transceiver which needs to be powered for access to the network, and thus to provide the lifeline feature discussed above, the RF transceiver must be powered by the cable distribution network which would constantly draw power, even while the subscriber unit is in the idle mode. The present cable power system cannot provide the necessary power required for the idle mode and would fail if a large number of subscriber units were active at the same time. A solution is to increase the power provided by the headend of the cable system to provide adequate power at the subscriber premise, or else provide premise powered subscriber units with battery back up for emergencies. The former requires a substantial redesign of the cable system to assure the voltages at the various subscriber premises, while the latter does not meet the goal of having the cable telephony system backwards compatible with existing telephone units.
Accordingly, it would be desirable to provide packet telephony power management of the cable distribution network for IP telephony between multiple subscriber units on a cable distribution network for packet telephony information between multiple subscriber units communicated over a public switch telephone network with at least one router on a communications network backbone.